In cellular communication networks, radio base stations (RBS) provide radio network coverage over a coverage area or cell. Communication links between the RBSs of a network and the communication network core segment are referred to as the backhaul. In traditional architectures, both radio and baseband processing are performed in the RBS, which outputs an Ethernet signal which is then transported over the backhaul using microwave and/or optical fibre.
In these traditional architectures where both radio and baseband processing are integrated in a single network element this network element is placed at the cell site. This requires power, real estate space, and relatively large cell towers. As cell sizes are getting smaller, more sites needs to be built and operated.
In some implementations, RBSs may be geographically separated into one or more Remote Radio Units (RU or RRU) and one or more baseband processing units, enabling, among other advantages, the optimising of radio unit placement. The scenario with architecture of a radio access network based on such a distributed Radio Base Station is widely identified as Centralized or Cloud Radio Access Network (CRAN). RRUs may be referred to as Radio Equipment (REs). The baseband processing units may be referred to as Digital Units (DUs) or as Radio Equipment Controllers (RECs). The communication links between REs and RECs in such deployments are collectively referred to as the fronthaul, and the interface between REs and RECs is referred to in the following description as the Fronthaul Interface (FHI). The Common Public Radio Interface (CPRI) specifies an interface protocol for the FHI, managing communication between REs and RECs. The latest version of the CPRI specification can be accessed here: http://www.cpri.info/downloads/CPR1_v_7_0_2015-10-09.pdf.
Novel radio splitting models are under definition to meet 5G high bandwidth demands, leveraging on different distribution of radio functions between antenna side equipment and centralized processing nodes. This will imply, for example, to move part of the radio processing back at the antenna side, especially for latency critical services.
In converged networks, encompassing both fronthaul and backhaul, as well as other kind of traffic, like OTN, CPRI traffic must be transported over long distances between the DU pool site and the RRUs or RBUs site (fronthaul is a term often used to identify this segment of the mobile traffic transport). Moreover, several switching nodes might be present between DU and RRU or RBUs sites. As discussed in earlier patent applications, PCT/EP2015/054502 and PCT/EP2015/077556, CPRI traffic has stringent latency, jitter and symmetry requirements and, for this reason, it requires special switching arrangements. In particular overall latency over the network shall be within about 100 μs (microseconds).
A number of transport options are under study, including packet based transport (e.g. based on Ethernet), to overcome CPRI bandwidth limitations. However, for some of these options latency requirements are similar to CPRI ones so that they also require special switching mechanisms for E2E latency control over the transport network.
It is important to note that the radio receivers expect the packets in the same sequence as they are transmitted. So all the packets of the same flow should follow the same E2E (end-to-end) path by designing the transport network not to change the packet sequence (e.g. assigning tunnels as in a regular packet network).